从嵌套映射中获取所有组合键

Question

我有一个嵌套的地图,如下所示:

val m: Map[Int, Map[String, Seq[Int]]] = 
  Map(
    1 -> Map(
      "A" -> Seq(1, 2, 3),
      "B" -> Seq(4, 5, 6)
    ),
    2 -> Map(
      "C" -> Seq(7, 8, 9),
      "D" -> Seq(10, 11, 12),
      "E" -> Seq(13, 14, 15)
    ),
    3 -> Map(
      "F" -> Seq(16, 17, 18)
    )
  )

我希望所需的输出显示Seqs中每个可能的整数组合.例如:

List((1, "A", 1),
     (1, "A", 2),
     (1, "A", 3),
     (1, "B", 4),
     (1, "B", 5),
     (1, "B", 6),
     (2, "C", 7),
     (2, "C", 8),
     (2, "C", 9),
     (2, "D", 10),
     (2, "D", 11),
     (2, "D", 12),
     (2, "E", 13),
     (2, "E", 14),
     (2, "E", 15),
     (3, "F", 16),
     (3, "F", 17),
     (3, "F", 18))

我一直在尝试使用map和flatMap的不同组合,但没有任何工作.有任何想法吗？

Answer 1

这是一种使用for comprehension的可能性:

for {
  (k1, v1) <- m
  (k2, v2) <- v1
  v3 <- v2
} yield (k1, k2, v3)

这遍历了m的所有顶部键/值对.对于每个这些最高值,这将遍历所有嵌套键/值.最后,对于所有这些嵌套值(列表),它会遍历每个元素并产生所请求的内容.

理解是等同于嵌套flatMap的,例如:

m.flatMap{
  case (k1, v1) => v1.flatMap {
    case (k2, v2) => v2.map(v3 => (k1, k2, v3))
  }
}